1. Field of the Invention
The present invention relates to hot melt ink for an ink jet printer and, more particularly, to hot melt ink for an ink jet printer which is solid at normal temperatures and is used for printing after being thermally melted at temperatures higher than normal temperatures.
2. Description of Related Art
Ink jet printers have many advantages in printing techniques, such as noiselessness, high speed, high quality and coloration. However, ink droplets jetted from a nozzle are directly deposited on recording paper, causing the print quality and print drying time to be influenced depending on the type of recording paper. If low-quality paper is used for recording, a considerable deterioration in quality of the resultant print has been experienced.
It is known that in order to solve the above problem, hot melt ink which has a melting point higher than room temperature is used, achieving print of a uniform dot size irrespective of the type of recording paper. Ink compositions that melt above room temperature have been proposed, including ink containing natural wax as disclosed in U.S. Pat. No. 4,390,369 ink containing stearic acid, as disclosed in European Unexamined Patent Publication No. 99,682, and ink containing a C.sub.20 -C.sub.24 acid or alcohol along with a ketone having a relatively high melting point, as disclosed in U.S. Pat. No. 4,659,383, in which all the inks make use of dyes as a coloring material. Moreover, in U.S. Pat. Nos. 4,659,383 and 4,822,418 hot melt inks are disclosed in which solid pigments are dispersed in waxes or C.sub.18 -C.sub.24 fatty acids having a melting point higher than 65.degree. C.
However, the known hot melt inks for ink jet printers described above have problems such as the degree of dye solubility when dyes are used as the coloring material. This limits the type of dyes that may be used. In addition, the ink cannot necessarily be kept as stabilized on heating over a long time or on repetition of heating and cooling cycles, coupled with another problem involved in the ink's color fastness to light. On the other hand, when pigments are used as the coloring material, good color fastness to light is attained but the pigment's dispersability and the stability of the dispersed pigment are not always satisfactory, with the unlikelihood that the ink's storage stability under heating conditions is good.